Cardiff easily beat 10-man Nottingham Forest 3-0 to go 12 points clear of third-placed Watford – who lost at Peterborough – with four matches remaining.
Rudy Gestede netted twice for the Welsh side, after Darius Henderson was dismissed for elbowing Heidar Helguson, who had scored the opener.
With the Bluebirds nine goals better off than the Hornets, Malky MacKay’s side would have to collapse spectacularly in the run-in.
Second-placed Hull were also victorious thanks to Robert Koren’s late strike giving them a 2-1 win at Ipswich Town.
Second-half substitute Koren headed home Robbie Brady's cross in the 83rd minute after Ipswich substitute Anthony Wordsworth had cancelled out Brady's first-half penalty.
The Tigers are now six points clear of Watford and would also have to fall to pieces to be relegated to the play-offs.
Watford’s surprise 3-2 defeat took struggling Peterborough out of the drop zone after extending their unbeaten run to eight matches.
Danny Swanson broke the deadlock and Dwight Gayle doubled their advantage on the hour mark. Lee Tomlin was instrumental in Gayle's goal and the two combined again for the third. The latter was brought down by last man Marco Cassetti, who was sent off, and Tomlin curled home a delicious free-kick.
Although Mark Yeates and Fernando Forestieri pulled back a couple of goals for the Hornets, it did not alter a result which has huge implications at both ends of the table.
Brighton got their play-off push back on track as they ended a three-match winless run with a comfortable 2-0 win away at free-falling Middlesbrough.
Two second-half goals from Spanish duo Andrea Orlandi and David Lopez secured the Seagulls their first away win in five attempts that moved them up to fifth in the npower Championship table.
For Tony Mowbray's Boro, they are down to 10th after their sixth defeat in their last seven games - and lie eight points off the top six, and just six points off the bottom three.
Bolton moved into the play-off places for the first time this season after substitute Craig Davies' late penalty earned a 2-1 win at lowly Bristol City.
Dougie Freedman's men went ahead inside the opening two minutes thanks to Liam Fontaine's own goal but were pegged back by Steven Davies' leveller after the break.
In an end-to-end second half, the visitors snatched a crucial three points when Craig Davies struck home the spot-kick after David Ngog was brought down in the area by substitute Matthew Bates.
Ludo Sylvestre fired his second goal in two matches in spectacular fashion as Blackpool secured a 1-0 Lancashire derby triumph over Burnley.
Sylvestre gave Pool the lead in their 1-1 draw with Nottingham Forest last weekend and he broke the deadlock with a superb long-range strike after 58 minutes.
Blackburn climbed out of the relegation zone by halting a 10-match winless run with a 2-0 home victory over Derby.
Jordan Rhodes scored his 26th Rovers goal of the season from the penalty spot to give the hosts an early lead.
Scott Dann's header in first-half injury time ensured Blackburn's first Championship win at Ewood Park in just over two months and condemned Derby to a 12th away league loss of the campaign.
Nine-man Barnsley dropped back in the relegation zone after their fine recent home form was ended in spectacular fashion - 6-0 by a rampant Charlton.
Seven wins from their last eight games at Oakwell had helped see the South Yorkshire side move out of the bottom three, but defeat against mid-table Charlton leaves them inside the drop zone, albeit one point behind Blackburn, who are 21st.
Bradley Pritchard, Johnnie Jackson, Yann Kermorgant, Callum Harriott, Salim Kerkar and Ricardo Fuller were all on target for Charlton, with Stephen Dawson and Tom Kennedy both dismissed for the Tykes.
Huddersfield came from behind to claim a 3-1 win and push Wolves further into relegation trouble. Midfielder Stephen Ward opened the scoring for Wolves but goals from Sean Scannell and Jermaine Beckford (2) gave Huddersfield an unassailable lead before Jamie O’Hara was sent off for raising his hands to Keith Southern.
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